In languages like English, the form of a verb is dependent on the properties of the subject. For instance, we say My brother laughs at these photographs but My brothers laugh at these photographs. The mechanism which provides the correct form of the verb is called agreement: in these sentences the verb agrees with the subject, and the difference in the form of the verb (laughs vs. laugh) is determined by the fact that the subject in one sentence is third person singular (my brother) whereas in the other it is third person plural (my brothers). The agreement between a verb and its arguments is a familiar and cross-linguistically frequent phenomenon, considered by many linguists, of different theoretical persuasions, to be at the core of language.
Another type of agreement familiar from English, is the agreement between a noun and its modifier: in the examples above these agrees with photographs in plural number (compare the singular alternative this photograph). Since the controller of the agreement, photographs is plural in both sentences, it is not surprising that the form of the demonstrative is also plural.
While verbs, adjectives, and demonstratives agree in many languages, a situation in which a preposition (such as at in the examples above) would change in any way is rather unusual. Still, there are languages, such as Welsh and Breton, where the form of a preposition changes depending on the grammatical properties of the noun it introduces.
A situation where the form of a preposition would change depending on the properties of the subject, as verbs do in English, and not with the noun it introduces as in Welsh, is so rare that it until now has escaped linguistic analysis altogether. To give an illustration: if in the example sentences above the preposition at had to appear in two forms: one in accordance with the singular number of the subject my brother and another in accordance with the plural number, my brothers, we would consider this to be a very unusual agreement pattern. This type of agreement does not respect the existing syntactic grouping in a sentence but connects elements which belong to different syntactic phrases (such as my brother and at). We call this pattern "external agreement". External agreement challenges existing syntactic models: all current approaches define agreement as a local syntactic relation, i.e. occurring within clear syntactic domain such as verb phrase, noun phrase, prepositional phrase, etc.
External agreement, being extremely rare typologically, appears with fascinating regularity in languages of the Nakh- Daghestanian family spoken in the Caucasus: there are 17 languages with diachronically unrelated instances of external agreement. Such an abundance of examples appearing in languages with considerable variation in their syntactic systems makes external agreement in Nakh-Daghestanian an ideal opportunity for research into morphosyntactic, semantic and pragmatic mechanisms which regulate not only agreement, a fundamental part of a grammar of many languages, but also the less obvious relationships between syntactic elements in a sentence.
Our previous work on agreement gives us the theoretical apparatus necessary for accounting for this challenging phenomenon. Our typological work makes us aware of the range of morphological and syntactic possibilities in agreement systems. Finally, our expertise in Nakh-Daghestanian languages in general enables us to go straight into the intricacies of external agreement patterns.
Our project will (i) investigate the phenomenon of external agreement from a theoretical perspective; (ii) collect new data from little studied and/or endangered languages; (iii) compile a database and make it fully available for public online use; and (iv) publish a book and articles on the significance of our findings for current theories of grammar.